The present invention relates generally to lithography, and particularly to optical photolithography glass for use in optical photolithography systems utilizing vacuum ultraviolet light (VUV) wavelengths below 193 nm, preferably below 175 nm, preferably below 164 nm, such as VUV projection lithography. systems utilizing wavelengths in the 157 nm region.
The invention relates to VUV transmitting glass that is transmissive at wavelengths below 193 nm, in particular, a photomask silicon oxyfluoride glass suitable for use in the Vacuum Ultraviolet (VUV) 157 nm wavelength region.
Refractive optics requires materials having high transmittance. For semiconductor applications where smaller and smaller features are desired at the248 and 193 nm wavelengths, high purity fused silica has been shown to exhibit the required transmittance of 99%/cm or better.
Projection optical photolithography systems that utilize the vacuum ultraviolet wavelengths of light below 193 nm provide benefits in terms of achieving smaller feature dimensions. Such systems that utilize vacuum ultraviolet wavelengths in the 157 nm wavelength region have the potential of improving integrated circuits with smaller feature sizes. Current optical lithography systems used by the semiconductor industry in the manufacture of integrated circuits have progressed towards shorter wavelengths of light, such as the popular 248 nm and 193 nm wavelengths, but the commercial use and adoption of vacuum ultraviolet wavelengths below 193 nm, such as 157 nm has been hindered by the transmission nature of such vacuum ultraviolet wavelengths in the 157 nm region through optical materials. Such slow progression by the semiconductor industry of the use of VUV light below 175 nm such as 157 nm light has been also due to the lack of economically manufacturable photomask blanks from optically transmissive materials. For the benefit of vacuum ultraviolet photolithography in the 157 nm region such as the emission spectrum VUV window of a F2 excimer laser to be utilized in the manufacturing of integrated circuits there is a need for glass that has beneficial optical properties including good transmission below 164 nm and at 157 nm and good durability and that can be manufactured economically.
The present invention overcomes problems in the prior art and provides economical high quality improved photomask blanks and VUV transmitting lithography glass that can used to improve the manufacturing of integrated circuits with vacuum ultraviolet wavelength
We have shown that dry, high purity fused silica ( less than 1 ppm OH) exhibits superior transmission in the deep ultraviolet compared to xe2x80x9cwetxe2x80x9d high purity fused silica (e.g., Coming Code 7980). With the addition of fluorine, the transmission of dry silica in the VUV can be even further improved. We have measured transmissions such as 79.8%/6.35 mm (90%/cm internal T) at 157 nm in these glasses. Such materials are of interest for use as components for 157 nm lithography, particularly photomask substrates, pellicles, thin lenses and windows. these applications, it is not only important that the glass exhibits a high initial transmission, but the transmission must not decrease under exposure to the F2 excimer laser. For 157 nm photomask material the glass preferably has  less than 1% transmission loss at 157.6 nm after exposure to the F2 excimer laser for 60 million at 0.1 mJ/cm2-pulse. Our invention describes silicon oxyfluoride glasses containing high levels of molecular oxygen that exhibit lower F2 laser-induced absorption compared to non-oxygen loaded glasses and methods for making them.
The invention includes a method of making a VUV transmitting glass for transmitting below 200 nm VUV wavelengths such as 157 nm wavelengths produced by F2 excimer laser. The method includes providing a silicon oxyfluoride glass, providing a plurality of O2 molecules, and doping the O2 molecules into the silicon oxyfluoride glass to provide a VUV transmitting silicon oxyfluoride glass containing intersticial O2 molecules.
The invention includes a method of making a laser durable VUV transmitting silicon oxyfluoride glass, which is preferably durable to F2 excimer laser exposure with a resistance to F2 laser induced absorption. The method includes providing a consolidated silicon oxyfluoride glass and providing an O2 doping treatment atmosphere. The method includes enveloping the silicon oxyfluoride glass with the O2 doping treatment atmosphere and dissolving a plurality of the O2 molecules from the atmosphere into the silicon oxyfluoride glass to provide a silicon oxyfluoride glass with in solution O2 molecules.
The invention includes a method of making a laser durable VUV transmitting silicon oxyfluoride glass. The method includes providing a non-consolidated silicon oxyfluoride glass precursor and providing a glass consolidation furnace with a heated consolidation zone for consolidating the non-consolidated glass precursor. The method includes supplying an oxygen doping atmosphere to the consolidation furnace and consolidating the glass precursor into a consolidated silicon oxyfluoride glass wherein O2 molecules are dissolved in the consolidated silicon oxyfluoride glass.
The invention includes a VUV transmitting glass photomask substrate. The photomask substrate is comprised of a silicon oxyfluoride glass doped with a plurality of O2 molecules.
The invention includes a VUV transmitting silicon oxyfluoride glass. The VUV transmitting silicon oxyfluoride glass contains a plurality of doped O2 molecules and has a resistance to VUV laser induced absorption bands.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principals and operation of the invention.